Air-root-pruning container

ABSTRACT

A vertical air-root-pruning container involving a series of vertical air gaps displaced around the sidewall of a container. The air gaps are alternately displaced outwardly or inwardly to air-prune spiral root growth in both the right and left directions or are equipped with deflecting means to make the pruning effect bidirectional. Such a container inhibits spiral growth, promotes root branching, and results in more even root distribution as well as increased root growth in the growing medium.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 309,085, filedNov. 9, 1981.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved nursery or greenhouse container orpot. More specifically, the invention relates to an apparatus and methodfor vertical air-root-pruning of plants grown in containers.

2. Description of the Prior Art

Plants have long been grown in pots in greenhouses and homes. Thepractice of producing large numbers of plants out-of-doors in containershas developed primarily since the early 1950's. The container nurseryindustry began in southern California and spread across the southernstates. The #10 food can with a few holes punched in the bottom waswidely used and soon became known as the "one gallon container". Duringthe sixties and seventies, the container nursery industry increasedrapidly for several reasons: (1) landscape plants grew at a faster ratein containers than in the field; (2) turnover time decreased; (3) theroot system of the plant remained undisturbed; thus, planting could bedone anytime, not just during the early spring as with bare root orballed-in-burlap nursery stock; and (4) ease of display and handlingmade container grown plants attractive to the consumer.

However, development of the container nursery industry was not withoutproblems. The complex nutritional requirements of plants grown incontainers took years to define. In addition, growing media was refineduntil the quality of plant growth in containers attained that of fieldgrown plants. The medium for the container evolved from field soil, tomixes of field soil and compost, to soilless mixes with far greater porespace for providing oxygen to the root system.

Numerous articles have been written and a common topic at gatherings ofnurserymen is root development, especially of woody plants, incontainers. As a root grows from a cutting or seedling in a container,its path is outward (towards the side of the container) and downward.When the root reaches the side of a round container it follows thecontour and generally after one half to one full circle, reaches thebottom where it may continue to elongate and circle, sometimes for fiveor more revolutions, all of which is considered to be deleterious to theplant.

In "Growth of Carissa qrandiflora `Boxwood Beauty` in varying media,containers, micronutrient levels", The Florida Nurseryman, 17(4):12-13,43 (1972), Whitcomb tried placing holes in the sides of containers toimprove root growth but without success (see also U.S. Pat. No.3,785,088). Later studies with tree seedlings grown in square bottomlesscontainers on a raised wire bench showed that air-root-pruning waseffective in stopping root elongation and wrapping at the bottom of thecontainer and, at the same time, in stimulating lateral branch rootdevelopment following the death of the root tip, Davis et al, "Effectsof Propagation Container Size on Development of High Quality TreeSeedling", Proc. Int. Plant Prop. Soc.; 25:448-453 (1975). More recentstudies showed that Bur oak trees (Quercus macrocarpa) grew larger anddeveloped a more fibrous root system in a square bottomless containerthan in a conventional round container of the same volume, Hathaway andWhitcomb, "The Effects of Root Malformation during Propagation on Growthand Survival of Bur Oak", Research Report P-760, Oklahoma AgriculturalExperimental Station, Oklahoma State University, pages 33-34 (1977).Unfortunately, growing plants in bottomless containers on raised wirebenches is neither practical nor economical. Birchell and Whitcomb,"Effects of Container Design on Root Development and Regeneration",Research Report P-760, Oklahoma Agricultural Experimental Station,Oklahoma State University, pages 39-45 (1977) compared the growth ofbirch trees grown in bottomless containers with vertical ribs on thesides. The vertical ribs stopped the circling or the wrapping of theroots of a fine, fibrous rooted species such as the birch. In addition,when the vertical ribs were present, there was no advantage to removingthe bottom of the container for air-pruning. Dickinson and Whitcomb,"Effects of Container Design on Root Quality", Research Report P-760,Oklahoma Agricultural Experimental Station, Oklahoma State University,pages 35-36 (1977) tried placing ribs across the bottom of a roundcontainer and vertical ribs one fourth to one half the height of thesidewall of the container in order that the container could be nestedfor stacking and shipping. Japanese black pine (Pinus thunberi ) andbald cypress (Taxodium distishum) trees were grown in these containersfor one growing season. The vertical ribs in the lower one fourth or onehalf of the container were effective in stopping circling of the pineroots; however, the more coarsely rooted cypress either bent the rib andcontinued to circle or was stopped by the rib from circling butcontinued to elongate creating a "tangled ball of string" effect.

Dickinson and Whitcomb, "The Effects of Spring Versus Fall Planting onEstablishment of Landscape Plants", S.N.A. Nursery Research Journal4(1):9-19 (1977) observed that the roots of container grown plants thatdeveloped following planting were extensions of roots that were alreadypresent in the container at the time of planting, and were not "new"roots. They suggest that the number of root tips present at plantingtime may be very important to the rapid establishment and frequently thesurvival of the container grown plants in the landscape.

These studies showed that the root system of a plant grown in acontainer could be improved (a) as in the case of bottomless containerson a wire bench and (b) that vertical ribs on the inside of thecontainer could improve the root structure of fine, fibrous rootedplants, but only worsened the problem for strong, coarsely rootedplants. Also, neither improvement was practical for the production ofnursery stock on a commercial scale.

SUMMARY OF THE INVENTION

In view of the problems associated with root development in plants grownin containers, I have discovered an improved container adapted tocontain a growing medium and a plant comprising:

(a) a bottom wall;

(b) a circumferential upwardly extending sidewall attached to theperimeter of the bottom wall thus forming an open-topped container; and

(c) one or more vertical air-root-pruning means displaced in thesidewall to air-prune roots of the plant thus inhibiting the tendency ofthe roots to grow in a spiral and stimulating additional root branching.

The present invention further provides that a plurality of verticalair-root-pruning means be a vertical slit in the sidewall with one edgeof the slit displaced outwardly or inwardly, and extending to the bottomof the container, thus creating an offset or air gap which prunes rootsdirected into the gap along the inner surface of the container. It isfurther provided that the outwardly or inwardly extending edges ofconsecutive slits distributed around the sidewall alternate between theright edge and the left edge such as to prevent spiraling of the rootsin both the clockwise and counterclockwise directions. Alternatively thepresent invention provides for a plurality of bidirectional verticalair-root-pruning means (effective from both directions) beingdistributed around the sidewall. Such a bidirectional means can beopenings at the corners of a square or rectangular cross-sectionalcontainer, a vertical opening with a V-shaped wedge on the inner side,or a vertical opening with a parallel recessed surface creating an innerair gap within the container.

Thus the present invention provides in a process for growing a plant ina growing medium contained in a pot having a bottom and acircumferential sidewall the specific improvement comprising the step ofair-pruning the roots of the plant along one or more vertical slits inthe sidewall thus inhibiting the tendency of the roots to grow in aspiral and stimulating additional root branching.

It is an object of the present invention to provide a container thatair-prunes the roots of the plant growing in the container. It is afurther object that this air-pruning take place along vertical regionsdistributed around the container sidewalls such as to prevent spiralroot growth and such as to promote root branching. It is a furtherobject that the container be consistent and essentially interchangeablewith containers presently used in the commercial container industry forgrowing plants. Fulfillment of these objects and the presence andfulfillment of other objects will be readily apparent upon completereading of this specification and claims taken in conjunction with theattached drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side view of a vertical air-root-pruning container accordingto the present invention.

FIG. 2 is a bottom view of the container of FIG. 1.

FIG. 3 is a side view of an alternate embodiment of the verticalair-root-pruning container according to the present invention.

FIG. 4 is a top view of the container of FIG. 3.

FIG. 5 is another alternate embodiment.

FIG. 6 is a photograph of root development of a pyracantha shrub grownin a container of the present invention on the left compared with onegrown in a conventional container on the right.

FIG. 7 is a close-up view of the root branching of the plant on the leftof FIG. 6.

FIG. 8 is a photograph of the root development, less the top of theplant and the growing medium, for the standard container ("S", left) andthe air-root-pruning container ("AP", right).

FIG. 9 is a side view of a bidirectional vertical air-root-pruningcontainer according to the present invention.

FIG. 10 is a top view of the container of FIG. 9.

FIG. 11 is a partial cut-away view showing an alternate embodiment of abidirectional vertical air-root-pruning means.

FIG. 12 is a bottom view of a bedding plant tray wherein each individualplant container in the tray contains bidirectional verticalair-root-pruning means.

FIG. 13 is a cross-sectional view of the container of FIG. 12 as seenthrough line 13--13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The air-root-pruning container of the present invention, how itfunctions and how it differs from other nursery stock containers canperhaps be best explained and understood by referencing the drawing.

FIGS. 1 and 2 illlustrate one embodiment of an air-root-pruningcontainer according to the present invention generally designated by thenumeral 10. The container 10 is made up of a circular flat bottom 12 andcircumferential upwardly extending sidewall 14 attached to the perimeterof the bottom 12. Displaced around the lower portion of the sidewall 14is a series of drain holes 16. As illustrated, four verticalair-root-pruning means 18 are evenly distributed around the sidewall 14(approximately every six inches for a one gallon container). With alarger container, say 12 inch diameter, there would need to be sixvertical slits to give optimum air-root-pruning. Likewise, in a smallerpot only two or three slits may be needed. Each verticalair-root-pruning means 18 involves making a cut or slit 20 vertically inthe sidewall 14, preferably extending to the bottom 12 of the container,with two horizontal cuts or slits 22 and 24 at either end of thevertical cut 20. The inner flap 26 created by the slits 20, 22 and 24 isthen pushed outward from the container 10 and held in this position byplacing or wedging a rigid rod 28 between the inner surface of flap 26and the outer surface of the sidewall above and below the flap 26. Thismay also be accomplished by allowing narrow sections of the plastic usedin the manufacture of the pot to remain in the slit and hold the slitopen as shown in FIG. 3. Alternately, the flap 26 can be pushed inwardand again held in place by a rigid rod or the like. In this manner avertical gap 30 is created which will air-prune the roots of the plantgrowing in the container, thus inhibiting the tendency for roots to growin a spiral. As shown, the vertical air gap 30 and flaps 26 arealternated such as to air-prune spiral root growth in both the right andleft (clockwise and counterclockwise) directions. The width of thevertical opening may be as narrow as one eighth inch or less forfine-rooted plants or as large as one fourth inch or more forcoarse-rooted plants.

FIGS. 3 and 4 illustrate an alternate embodiment wherein theair-root-pruning means 32 are molded directly into the container. Inthis embodiment, the sidewall is made up of two pairs of concentricquadrants 38 and 40 of slightly different and alternating radii.Vertical openings 42 present in the narrow vertical radial walls 44located between the adjacent concentric sidewall quadrants 38 and 40 areequivalent to the air-root-pruning gaps of FIGS. 1 and 2. FIG. 5illustrates still another embodiment wherein the verticalair-root-pruning means are staggered about and molded into the sidewallof the container. The vertical openings in the container sidewall do nothave to be continuous from top to bottom to be effective. Some sectionsof the vertical sidewall may remain in place to add strength to thecontainer.

FIGS. 9 and 10 illustrate a particularly preferred embodiment whereinthe air-root-pruning means 46 is bidirectional in its pruning effect.This bidirectional feature is accomplished by providing each verticalopening 48 in the sidewall 50 of the container with a V-shaped insert52. The V-shaped inserts are positioned such that the point of the V isdirected outward through the opening 48. In this manner, the spirallingroot upon encountering the sloped sides of the V-shaped member 52 willbe directed toward the air gap resulting in air-root-pruning. FIG. 11illustrates an alternate embodiment of the bidirectionalair-root-pruning means wherein a relatively wider opening 54 is providedwhich is backed with an inner parallel surface 56 thus creating air gaps58 and 60. Again, a root growing along the inside of the container willbe directed into an air gap whether spiralling is clockwise orcounterclockwise. FIGS. 12 and 13 illustrate still another embodiment ofthe bidirectional air-root-pruning means involving a square orrectangular cross-sectioned multicompartmented bedding plant tray 62.The vertical corners 64 of each rectangular compartment are partiallyremoved forming openings 66 and 68 that air prune the roots approachingfrom either side.

EXAMPLE

In order to demonstrate the beneficial effects of vertical air-pruningaccording to the present invention, Pyracantha X `Mojave` plants weregrown in standard pots and in air-root-pruning containers of equal sizeunder identical and simultaneous growing conditions for three months. Atthe end of this period some of the plants were removed from theirrespective containers and were visually examined and photographed. FIG.6 is a photograph of the root development of a pyracantha shrub grown ina container with vertical slits (left) and one grown in a conventionalround two gallon container (right). Some of the roots in theconventional container circle halfway or more around the container eventhough the plant was only three months old. FIG. 7 is a close-upphotograph of the root development of the pyracantha shrub shown on theleft in FIG. 6. The root development is stopped at the vertical slits inthe sides of the containers and branching of the root behind the tip isstimulated. FIG. 8 is a photograph of root development, less the top ofthe plant and the growing medium, of the pyracantha plant grown in thestandard pot (left) and grown in the air-root-pruning container (right).It can be observed that greater root growth has occurred in theair-root-pruning container.

In order to quantitatively establish the observed differences in plantgrowth, the number of branches per plant was counted and the weight oftop growth and root growth was measured for a representative set ofplants. A second representative set of each type of container grownplant was transplanted into larger containers and allowed to grow for anadditional ten (10) days under identical conditions. The plants werethen removed from the larger containers such that the number to two inchlong roots could be counted. The respective data are presented in TABLEI below.

                  TABLE I                                                         ______________________________________                                        Effects of vertical air-root-pruning on                                       growth of Pyracantha X `Mojave`                                                         Standard Pot                                                                           Air-Prune Pot                                                                             % Increase                                     ______________________________________                                        Branches/plant                                                                            12.5       32.5        158%                                       No. of roots 2"                                                                           44         126         187%                                       long 10 days after                                                            transplant                                                                    Top weight (g)                                                                            93.3       152          63%                                       Root weight (g)                                                                           109        192          38%                                       ______________________________________                                    

As clearly indicated by the data, all critical growth parametersquantitatively favor the use of the air-root-pruning container. Withplants grown in the conventional container, only a few rot tips exist atthe bottom of the container (see FIG. 6). At the time of planting in thelandscape, these root tips extend into the surrounding soil. Thus, inthe case of the plant grown in the vertical air-root-pruning container,the marked increase in the number of root tips existing at planting timeresults in accelerated establishment of the plant in the landscape. Themore even distribution of root development throughout the containermedium, instead of most roots developing in a spiral pattern on the verybottom of the container, further promotes accelerated establishment ofthe plant. Stimulated branch root development enhances further plantgrowth by increasing the root surface area which in turn promotesincreased absorption of water and nutrients.

Additional advantages associated with the use of the air-root-pruningcontainer of the present invention include the fact that the containerhas a conventional bottom for ease of filling, handling, and shipping.The containers can be filled by existing commercial pot fillers withoutmodification. And, the containers will nest or stack such that freightcosts for shipping the containers from manufacturers to nurserymen isnot increased.

Having thus described the preferred embodiments with a certain degree ofparticularity, it is manifest that many changes can be made in thedetails of construction, arrangement and fabrication of the elementswithout departing from the spirit and scope of the invention. Therefore,it is to be understood that the invention is not limited to theembodiments set forth herein for purposes of exemplification, but is tobe limited only by the scope of the attached claims, including the fullrange of equivalents to which each element thereof is entitled.

I claim:
 1. A container adapted to contain a growing medium and a plantcomprising:(a) a bottom wall; (b) a circumferentially upwardly extendingsidewall attached to the perimeter of said bottom wall thus forming anopen-topped container; and (c) one or more vertical air-root-pruningmeans displaced in said sidewall forming an off-set air gap to air-pruneroots of said plant thus inhibiting the tendency of said roots to growin a spiral and stimulating additional root branching and wherein atleast one of said air-root-pruning means is bidirectional.
 2. Acontainer of claim 1 wherein said bidirectional air-root-pruning meansis a vertical opening containing a V-shaped wedge.
 3. A container ofclaim 1 wherein said bidirectional air-root-pruning means is a verticalopening with a parallel surface displaced within said container.
 4. Acontainer of claim 1 wherein said bidirectional air-root-pruning meansis a vertical opening at each corner of a square or rectangularcross-sectioned container.
 5. A container of claim 1, 2, 3, or 4 whereinthere are four of said vertical air-root-pruning means.
 6. In a processfor growing a plant in a growing medium contained in a pot having abottom and a circumferential sidewall, the specific improvementcomprising the step of air-pruning roots of said plant along a pluralityof vertical slits distributed around said sidewall thus inhibiting thetendency of said roots to grow in a spiral and stimulating additionalroot branching and wherein said plurality of vertical slits distributedaround said sidewall sequentially have alternating right and then leftedges displaced outwardly or inwardly to said container thus air-pruningboth the clockwise and counterclockwise spiral growth of said roots. 7.In a process for growing a plant in a growing medium contained in a pothaving a bottom and a circumferential sidewall, the specific improvementcomprising the step of air-pruning roots of said plant along at leastone vertical slit in said sidewall thus inhibiting the tendency of saidroots to grow in a spiral and stimulating additional root branchingwherein said air-root-pruning is performed bidirectionally at saidvertical slit.
 8. A process of claim 7 wherein said air-pruning isperformed at a plurality of bidirectional vertical slits distributedaround said sidewall.
 9. A container adapted to contain a growing mediumand a plant comprising:(a) a substantially square or rectangular bottomwall; (b) upwardly extending sidewalls attached to the perimeter of saidsquare or rectangular bottom wall thus forming an open-topped containerhaving a substantially square or rectangular cross-section; and (c) oneor more bidirectional vertical air-root-pruning means located at cornersof said substantially square or rectangular cross-section container.